This invention relates to a fault diagnosis system for hydraulic pumps in a work vehicle equipped with a plurality of variable displacement hydraulic pumps as the hydraulic pumps and adapted to perform work by driving a plurality of hydraulic actuators. The fault diagnosis system determines whether each of the variable displacement hydraulic pumps is operating properly or not operating properly.
A work vehicle such as a hydraulic excavator performs given work by driving a hydraulic pump with an engine and driving a hydraulic actuator with pressurized fluid delivered from the hydraulic pump. Development of a trouble in the hydraulic pump therefore causes a serious problem or inconvenience for the work by the work vehicle. It is hence important to determine whether the hydraulic pump is operating properly or not operating properly and, if a trouble is determined to have been developed, to promptly carry out a repair such as replacement of a component so that the problem or inconvenience for the work can be minimized. Determination as to whether a hydraulic pump is operating properly or not operating properly (a fault diagnosis) has heretofore been effected by measuring with a flow meter a flow rate of pressurized fluid delivered from the hydraulic pump and checking whether or not the flow rate falls within a predetermined range.
Examples of the flow meter include a turbine flow meter, an oval flow meter, a flow meter making use of a Pitot tube, and a flow mater disclosed in Japanese Patent Application No. SHO 63-113434 and adapted to detect a displacement of a poppet valve. These flow meters are all accompanied by problems that they are complex in structure, high in price and poor in vibration resistance. Accordingly, mounting of such a flow meter on a small hydraulic pump installed at a slightly-vibrated place is feasible, but mounting of such a flow meter on a hydraulic pump of a work machine subjected to large vibrations such as a hydraulic excavator is practically infeasible. It is therefore the current circumstances that, concerning a hydraulic pump of a work vehicle subjected to large vibrations, a predetermined use period is set for each of components making up the hydraulic pump and the component is replaced by a corresponding new component at a suitable time after expiration of the use period.
The use period is however set with a substantial allowance, so that the component can be used for a further period without replacement in many instances. The above-mentioned practice of component replacement is hence not preferred from the viewpoint of economy and also from the viewpoint of labor and time required for the component replacement. Described specifically, a large hydraulic excavator is generally equipped with many hydraulic pumps, and pressurized fluids delivered from two of the hydraulic pumps are combined to drive a hydraulic actuator. If any one of these hydraulic pumps develops a trouble, an operator can become aware of the development of the trouble by a change in the actuation speed of the associated hydraulic actuator. When the hydraulic actuator is driven by combining pressurized fluids delivered from two hydraulic pumps, it is impossible to determine which one of the hydraulic pumps has developed a trouble even when development of a trouble on the side of the hydraulic pumps is found from a change in the actuation speed of the hydraulic actuator. To determine which one of the hydraulic pumps has developed the trouble, it is necessary to suspend the operation of the large hydraulic excavator and then to inspect the above-mentioned trouble. This operation suspension of the large hydraulic excavator however leads to a significant reduction in the efficiency of the work.
An object of the present invention is therefore to provide a fault diagnosis system for hydraulic pumps in a work vehicle, which can overcome the above-described problems of the conventional art, does not use flowmeters, is economical, and permits sure identification of one or more trouble-developed ones of the hydraulic pumps.